TDP-43 multidomains and RNA modulate interactions and viscoelasticity in biomolecular condensates
Pith reviewed 2026-05-22 18:33 UTC · model grok-4.3
The pith
RNA binding to TDP-43 replaces some protein-protein contacts with protein-RNA contacts and shifts condensate viscosity and elasticity.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Our analysis reveals that interaction sites within the IDR undergo dynamic rearrangement, driven by key residues that depend on the specific combination of folded domains. Upon RNA binding, several intermolecular interactions of TDP-43 are replaced by TDP-43-polyA interactions, altering viscoelastic properties of the condensate. Specifically, RRMs enhance viscosity, whereas the NTD reduces it. The presence of polyA increases elasticity, making viscosity and elasticity comparable in magnitude. These findings suggest that the multidomain structure of TDP-43 and its RNA interactions orchestrate condensate organization, modulating their viscoelastic properties.
What carries the argument
Dynamic rearrangement of interaction sites inside the IDR, controlled by the combination of RRMs, NTD, and polyA RNA.
If this is right
- RRMs raise the viscous response of the condensate.
- The NTD lowers the viscous response of the condensate.
- PolyA RNA raises elasticity until it becomes comparable to viscosity.
- The specific mix of domains and RNA determines which residues dominate the rearranged interaction network.
Where Pith is reading between the lines
- Cells could adjust condensate mechanics by altering the relative expression of TDP-43 domains or the local RNA concentration.
- Analogous domain-RNA competition may set material properties in condensates formed by other multidomain RNA-binding proteins.
- Domain-specific mutations could be introduced in vitro to test whether targeted changes in viscosity or elasticity alter condensate fusion or cargo retention.
Load-bearing premise
The molecular-dynamics force fields and simulation lengths used here correctly reproduce the real dynamic rearrangement of interaction sites and the resulting macroscopic viscoelastic response.
What would settle it
A microrheology or oscillatory measurement on TDP-43 condensates that finds no increase in the ratio of elastic to viscous moduli when polyA is added, or no opposite viscosity shifts when RRMs or NTD are removed.
Figures
read the original abstract
RNA-binding proteins form biomolecular condensates with RNA through phase separation, playing crucial roles in various cellular processes. While intrinsically disordered regions (IDRs) are key drivers of phase separation, additional factors such as folded domains and RNA also influence condensate formation and physical properties. However, the molecular mechanisms underlying this regulation remain elusive. Here, using molecular dynamics simulations, we investigate how the multidomain structure of TDP-43, which consists of its IDR, RNA recognition motifs (RRMs), and N-terminal domain (NTD), interacts with RNA and affects the characteristics of phase separation. Our analysis reveals that interaction sites within the IDR undergo dynamic rearrangement, driven by key residues that depend on the specific combination of folded domains. Upon RNA binding, several intermolecular interactions of TDP-43 are replaced by TDP-43-polyA interactions, altering viscoelastic properties of the condensate. Specifically, RRMs enhance viscosity, whereas the NTD reduces it. The presence of polyA increases elasticity, making viscosity and elasticity comparable in magnitude. These findings suggest that the multidomain structure of TDP-43 and its RNA interactions orchestrate condensate organization, modulating their viscoelastic properties.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript uses molecular dynamics simulations to examine how the multidomain architecture of TDP-43 (IDR, RRMs, and NTD) interacts with polyA RNA and modulates intermolecular contacts and the viscoelastic properties of biomolecular condensates. It reports dynamic rearrangement of IDR interaction sites depending on the presence of folded domains, replacement of TDP-43 intermolecular interactions by TDP-43-polyA contacts upon RNA binding, RRMs increasing viscosity, the NTD decreasing viscosity, and polyA increasing elasticity until the two moduli become comparable in magnitude.
Significance. If the reported domain-specific effects on viscosity and elasticity are robust, the work would provide useful molecular insight into how folded domains and RNA tune condensate mechanics in TDP-43 systems, with potential relevance to ALS/FTD pathology. The direct linkage of specific domains to changes in interaction networks and macroscopic moduli is a positive feature, though the absence of methodological validation for the viscoelastic calculations limits current impact.
major comments (2)
- [Methods] Methods section: No force field, system size, equilibration protocol, or error estimation procedure is described for the MD trajectories used to compute viscosity and elasticity. This is load-bearing because force-field inaccuracies in π–π or cation–π contacts are known to invert relative interaction strengths in IDR condensates, directly affecting the claimed replacement of TDP-43 contacts by TDP-43-polyA interactions and the domain-specific viscosity trends.
- [Results] Results (viscoelastic properties subsection): The manuscript provides no data on the length of the production trajectories or on whether the stress autocorrelation functions have decayed to yield converged zero-shear viscosity and storage modulus. Given that relaxation times in disordered-protein condensates frequently exceed 1 µs, this omission prevents assessment of whether the reported comparability of viscosity and elasticity upon polyA addition is reliable or an artifact of insufficient sampling.
minor comments (2)
- [Abstract] Abstract: The abbreviation 'polyA' should be expanded on first use for clarity.
- [Figures] Figure captions: Several panels lack error bars or indication of the number of independent runs used to generate the reported interaction counts and modulus values.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed comments, which have helped us identify areas where the manuscript can be improved for greater clarity and rigor. We have revised the manuscript to address the concerns about methodological details and the validation of viscoelastic calculations.
read point-by-point responses
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Referee: [Methods] Methods section: No force field, system size, equilibration protocol, or error estimation procedure is described for the MD trajectories used to compute viscosity and elasticity. This is load-bearing because force-field inaccuracies in π–π or cation–π contacts are known to invert relative interaction strengths in IDR condensates, directly affecting the claimed replacement of TDP-43 contacts by TDP-43-polyA interactions and the domain-specific viscosity trends.
Authors: We agree that these methodological details were insufficiently described in the original submission. In the revised manuscript, we have substantially expanded the Methods section to specify the force field, system sizes and compositions for each construct, the full equilibration and production protocols, and the error estimation procedures (including block averaging across independent replicas). We have also added a brief discussion acknowledging known limitations of current force fields for π–π and cation–π interactions while emphasizing that our primary conclusions rely on relative changes across domain combinations and RNA conditions rather than absolute interaction energies. revision: yes
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Referee: [Results] Results (viscoelastic properties subsection): The manuscript provides no data on the length of the production trajectories or on whether the stress autocorrelation functions have decayed to yield converged zero-shear viscosity and storage modulus. Given that relaxation times in disordered-protein condensates frequently exceed 1 µs, this omission prevents assessment of whether the reported comparability of viscosity and elasticity upon polyA addition is reliable or an artifact of insufficient sampling.
Authors: We thank the referee for this important observation. In the revised manuscript, we now report the lengths of the production trajectories and include supplementary figures of the stress autocorrelation functions demonstrating their decay. We have added text confirming that the functions reach near-zero values within the sampled time and that the resulting zero-shear viscosity and storage modulus values are stable when computed over different trajectory segments, supporting the reliability of the observed shift toward comparable viscosity and elasticity upon polyA addition. revision: yes
Circularity Check
No circularity: claims rest on direct MD simulation outputs
full rationale
The paper reports molecular dynamics simulations of TDP-43 multidomain constructs with and without polyA RNA. Interaction rearrangements and viscoelastic changes (RRMs increasing viscosity, NTD decreasing it, polyA increasing elasticity) are extracted as direct observables from the trajectories. No equations, fitted parameters, or self-citations are presented that redefine inputs as outputs or force predictions by construction. The derivation chain is computational and self-contained against external benchmarks such as force-field validation and experimental condensate rheology; it does not reduce to tautological renaming or self-referential fitting.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Standard biomolecular force fields and simulation protocols sufficiently reproduce the equilibrium structure and dynamics of TDP-43-RNA condensates on accessible timescales.
Reference graph
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discussion (0)
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